Fins have been used for some time in the ordnance field to stabilize kinetic energy (KE) projectiles in flight. After the projectile exits the gun tube, aerodynamic spin is induced by canted control surfaces on the fin blades. This spin is necessary to stabilize the projectile and reduce yaw. Reducing the total yaw is extremely important in order to maximize terminal ballistic performance on target. Stabilizing the projectile gives a repeatable ballistic trajectory with a tighter dispersion pattern on target and a higher probability of hitting a target at range. For fin stabilized projectiles, fin damage will destabilize aeroballistic flight and induce yaw.
The main damage to KE projectile fins often occurs inside the gun tube, due to fin impact with propellant granules inside the cartridge during projectile acceleration and the high propellant flash temperatures. Additional damage to the fins is possible due to fin aerodynamic heating outside the gun tube. Fin impact damage occurs at the leading edge of the fins, and creates an irregular fin leading edge shape such as a saw tooth-like ragged edge. This is particularly evident on aluminum fins. Steel fins, because they are inherently heavier, are usually made thinner to compensate for their increased weight, which also makes them susceptible to impact damage.
Although minor fin damage may not be detrimental to projectile accuracy, a significant leading edge damage, which is generally not symmetric for all fins, can cause side forces on the projectile, and can alter the intended steady state spin for projectiles with chamfered fin leading edge surfaces intended for producing spin.
Coating the fins with a thin, hard protective material only helps their heat resistance to burning and ablation during flight. Thin coating, however, does not greatly help protect against the direct impact damage due to propellant granules. The use of long, stick-type propellant may eliminate some impact damage, but is not desirable because it does not fill all the space around the projectile tail-end in its propellant case.
One prior art device to protect fins is shown in U.S. Pat. No. 5,062,585, which shows a fixed-in fin heat sink shield represented by a detached or attached additional fin piece to the original projectile fin. This added fin piece can help only in reducing the leading edge heating damage (during flight when out of the gun tube) but not the impact damage inflicted by the powder granules. Another prior art device is shown in U.S. Pat. No. 4,936,219, which shows a one-piece protection concept covering both the base and the whole fins of a projectile. U.S. Pat. No. 5,474,256, shows a glove-type fin cover made of combustible material to protect the fin and will be burned before exiting the gun muzzle.